Motor driving circuit

Abstract

A motor driving circuit drives a motor on receipt of an error signal having a digital value corresponding to a deviation between a current rotation speed of the motor, which is the subject to be driven, and its target value. A digital filter eliminates a high-frequency component of the error signal. A driving unit controls an electric current flowing through the motor in accordance with the digital value of the error signal from which the high-frequency component is eliminated by the digital filter. An upper-limit value setting unit sets an upper limit value to the digital value of the error signal input to the digital filter. The upper-limit value setting unit is configured to be capable of changing the upper limit value in accordance with a setting signal from the outside.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a motor driving technique, and more particularly to a control technique of a rotation speed (frequency) of a motor.[0003]2. Description of the Related Art[0004]A motor driving apparatus that drives a DC (direct current) motor or a spindle motor with a desired rotation speed monitors the rotation speed of the motor so as to produce a driving signal on the basis of the deviation from a desired target value. The motor driving apparatus that controls a motor as described above may employ a speed discriminator disclosed in the Japanese Patent Application (Laid-Open) No. H06-30589, for example.[0005]Some of the speed discriminators compare a current rotation speed of the motor and a rotation speed that is a desired target value, and outputs an error signal according to the deviation as a digital value. This error signal produces a pulse-width modulation signal having a duty ratio according to ...

AI Technical Summary

Benefits of technology

[0007]The present invention is accomplished in view of the above-mentioned problem, and a general purpose thereof is to provide a motor driving technique that suppresses the increase in the circuit size and has enhanced starting characteristic.

[0009]Immediately after the starting of the motor, the deviation between the current rotation speed of the motor and its target value becomes large, so that the digital value of the error signal increases with the increased deviation. However, according to this embodiment, an upper limit value is set to the digital value, whereby the input value of the digital filter does not sharply increase. Therefore, an overshoot in which the rotation speed of the motor greatly exceeds the target value can be prevented, and the starting characteristic of the motor can be improved. Since it is unnecessary to increase the sampling frequency in this embodiment, the increase in the circuit size can be suppressed. It is to be noted that the “upper limit value” means a value lower than the maximum value that the error signal can take in the state where the upper limit value is not set, and the maximum value that the error signal can take in the state where “the upper limit value is set” is its upper limit value.

[0010]The error signal is m-bit (m is a natural number), and the upper-limit value setting unit may invalidate the high-order n-bit (n is a natural number satisfying n<m) of the digital value. The upper limit value can easily be set by invalidating the high-order n-bit among m bits of the error signal.

[0014]Since the output of the infinite impulse response filter gradually approaches a value determined by the error signal input to the digital filter from the set initial value in this case, it is prevented that the output of the digital filter is set sharply to a great value upon the starting, whereby the overshoot of the rotation speed of the motor can be prevented.

[0018]According to this embodiment, the starting characteristic of the motor can be improved, while suppressing the increase in the circuit size of the motor driving apparatus.

[0020]According to this embodiment, the starting time taken for the rotation speed of the motor to reach the target value can be shortened, whereby the movable unit of the electronic apparatus can be operated with increased speed.

Problems solved by technology

Specifically, as the sampling frequency of the error signal is high, the characteristic of the digital filter is improved, thereby providing an advantage that the transient response, e.g., the starting characteristic of the motor can be improved, but causing a problem that the circuit size of the digital filter increases.

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